Project Summary Interferon e (IFNe) is a critical innate immune mediator that protects the host against sexually transmitted infections. Although the current paradigm is that IFN? is a type I IFN and signals through IFNa receptors, our and other published results show that IFN? has unique immune functions that are distinct from IFNa/b. IFN? is highly abundant in the mucosa of the female reproductive tract, and has superior mucosal immune activity compared to IFNa/b. IFNe gene expression is regulated by estrogen, cytokines, and seminal plasma, but is not induced by Toll-like receptor pathways, which induce IFNa/b. Clinical evidence indicates a protective role of IFNe against HIV. IFNe expression is positively associated with estrogen levels during the menstrual cycle, and inversely correlates with HIV susceptibility. Importantly, HIV-negative sex workers with frequent exposure to semen have an increased level of IFNe gene expression, and have increased numbers of immune effector cells in cervical tissues. We recently demonstrate that IFNe induces an anti-HIV state through a mechanism independent of known type I IFN-induced HIV host restriction factors in primary macrophages. Additionally, IFN? elicits a more robust immune response than IFNa2. We hypothesize is that IFNe displays a dual role in HIV inhibition by protecting HIV target cells and by modulating immune functions, and will test our hypothesis by determining the immune mechanism of IFNe and its impact on HIV infection in vitro, cervical explants and in humanized mouse model. To gain a better understanding of the molecular mechanism of IFNe-mediated HIV inhibition, we determine viral determinants important for IFNe sensitivity. Because estrogen is known to modulate IFNe expression and mucosal immunity, we will assess the impact of estrogen on IFN?-mediated processes in HIV infection in postmenopausal women before and after estrogen treatment. Elucidating the properties and functions of IFNe promises to expand our knowledge of virus-host interactions crucial for HIV prevention and control of viral reservoirs and immunopathogenesis.